The present invention relates to an electrophotographic image forming apparatus that transfers a toner image to a sheet of paper by using a plurality of image formation elements including a photoreceptor.
Some electrophotographic image forming apparatuses primarily transfer a toner image formed on a photoreceptor to an intermediate transfer element, and then secondarily transfer the toner image from the intermediate transfer element to a sheet of paper. Generally, the bearing surface of the photoreceptor after a primary transfer and the bearing surface of the intermediate transfer element after a secondary transfer will be subjected to cleaning with a cleaning element to prepare for the next toner image formation and primary transfer. In cleaning, since the cleaning elements, such as a blade, contact the bearing surfaces of the photoreceptor and the intermediate transfer element, there is a possibility that the shortage of the amount of residual toner which remains on the bearing surfaces may damage to the bearing surfaces.
Accordingly, in relation to the cleaning of the intermediate transfer element, the image forming apparatus disclosed in Japanese Patent Laid-Open Publication No. 2006-251138 transfers a cleaning toner image (a toner band) to an intermediate transfer element of which a bearing surface revolves. By forming a toner band in cleaning the bearing surface of the intermediate transfer element, sufficient amount of toner is replenished to the bearing surface of the intermediate transfer element and damage of the bearing surface due to the contact of a cleaning element can be prevented. This technology can be also applied to when a photoreceptor is cleaned, and can prevent the bearing surface of the photoreceptor from being damaged by forming a toner band for photoreceptors.
In addition, onto the surface of a secondary transfer element disposed so as to face the bearing surface of the intermediate transfer element with a sheet of paper held therebetween in a secondary transfer position, the toner which has remained on the bearing surface of the intermediate transfer element may be transferred, and when the transferred toner is left as it is, the reverse side of the sheet will be contaminated or stained. Therefore, the surface of the secondary transfer element also needs to be cleaned with a cleaning element and one conceivable approach in order to prevent the surface of the secondary transfer element in cleaning from being damaged is to form a toner band for the secondary transfer element.
However, when a toner amount necessary in order to prevent damages to the bearing surface of the intermediate transfer element is replenished at a time with a single toner band, excess of the toner starts leaking downstream of the cleaning element in a moving direction of the intermediate transfer element, and, on the contrary, contaminates and stains the intermediate transfer element. On the other hand, when the necessary toner amount is replenished with a plurality of toner bands intermittently formed along the moving direction of the bearing surface of the intermediate transfer element, the cleaning will take longer.
In particular, the cleaning takes much longer when a toner band is formed for each of the plurality of image formation elements such as a photoreceptor, an intermediate transfer element, and a secondary transfer element.
In view of these problems, an object of the present invention is to provide an image forming apparatus capable of efficiently forming a toner band for each of a plurality of image formation elements, and preventing cleaning of the plurality of image formation elements from taking longer.